Revert of Remove more unretained

Revert of Remove more unretained (https://codereview.chromium.org/322233002/)

Reason for revert:
Appears to have broken WallpaperManagerPolicyTest.PRE_PRE_WallpaperOnLoginScreen on http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%28dbg%29%281%29/builds/30930

[30103:30164:0613/224522:FATAL:weak_ptr.cc(26)] Check failed: sequence_checker_.CalledOnValidSequencedThread(). WeakPtrs must be checked on the same sequenced thread.
#0 0x7f486887bd6d base::debug::StackTrace::StackTrace()
#1 0x7f48688f8581 logging::LogMessage::~LogMessage()
#2 0x7f4868914936 base::internal::WeakReference::Flag::IsValid()
#3 0x7f4868914a03 base::internal::WeakReference::is_valid()
#4 0x000002f40b7e base::WeakPtr\u003C>::get()
#5 0x000002f3e405 base::internal::InvokeHelper\u003C>::MakeItSo()
#6 0x000002f3a45f base::internal::Invoker\u003C>::Run()
#7 0x7f486886685b base::Callback\u003C>::Run()
#8 0x7f48689bf4fd base::SequencedWorkerPool::Inner::ThreadLoop()
#9 0x7f48689bdd83 base::SequencedWorkerPool::Worker::Run()
#10 0x7f48689c9704 base::SimpleThread::ThreadMain()
#11 0x7f48689bc575 base::(anonymous namespace)::ThreadFunc()
#12 0x7f48647dde9a start_thread
#13 0x7f4861d733fd clone

Original issue's description:
> Remove more unretained
> 
> BUG=349083
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=277137

TBR=bshe@chromium.org,oshima@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=349083
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=277224

[please use gerrit instead, 2014-06-14 15:51:54]

Created Revert of Remove more unretained

[commit-bot: I haz the power, 2014-06-14 15:53:24]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/rouslan@chromium.org/331033002/1

[commit-bot: I haz the power, 2014-06-14 15:54:32]

Change committed as 277224